Technical Abstract:
Escherichia coli O157:H7 (EcO157) causes severe disease including hemolytic uremic syndrome and contributes significantly to human infections and outbreaks. We previously reported that natural curli variants isolated from the same strain display distinct phenotypic differences: curli-deficient variants (C-) were more acid resistant than their corresponding curli-producing variants (C+), whereas C+ variants grew better than C- variants under nutrient-limited conditions. To understand the molecular basis of the physiological differences between the natural EcO157 curli variants, we applied microarray-based transcriptomic analysis to compare global gene expression in EcO157 curli variants that were isolated from strains linked to the 2006 spinach outbreak and to the 1993 hamburger outbreak. We found that a total of 133 common genes were expressed differently in all three pairs of EcO157 curli variants, of which, 35 and 98 genes were up-regulated in C+ and C- variants, respectively. As predicted, genes involved in biogenesis of curli fimbriae were highly expressed in C+ variants. The transcription of the csgA gene in the C+ variants was 4.3- and 60.2 fold higher than in the corresponding C- variants isolated from the 2006 spinach outbreak strain and from 1993 hamburger outbreak strain, respectively, which correlated with the production of CsgA in these two C+ variants, as detected by Western analysis. Additionally, several genes involved in fatty acids transport and metabolism were up-regulated in C+ variants including genes fadBA, fadD, and fadL. Among up-regulated genes in C- variants, many were involved in protein synthesis and stress tolerance. For example, considerable induction levels were observed for genes encoding the acid resistance proteins HdeB, HdeA, HdeD, and components of the acid resistance system 2, glutamate decarboxylase (GadA) and the corresponding anti-transporter (XasA). Our data suggest there are distinct differences in global gene expression between the EcO157 curli variants. Enhanced expression of acid resistance genes in C- variants may explain partly the distinct differences in acid resistance between the natural curli variants isolated from the same EcO157 strain.